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Oliver Sacks Travels Down “The River of Consciousness”

Madagascar’s star orchid intrigued Darwin. He inferred a moth must exist that could reach its nectar.

After roiling the world by publishing his book “On the Origin of Species,” Charles Darwin retreated to his estate’s conservatories, not to putter about in retirement but to seek further evidence for his theory of evolution by natural selection. His greenhouses became, in the words of Oliver Sacks, “engines of war, from which he would lob great missiles of evidence at the skeptics outside.”

Sacks, the neurologist and writer who died in 2015 at age 82, relished writing about Darwin. “The River of Consciousness,” a collection of 10 previously published essays, reveals Sacks as a gleeful polymath and an inveterate seeker of meaning in the mold of Darwin and his other scientific heroes Sigmund Freud and William James.

In honor of the anniversary of the publication of Darwin’s Origin of Species on November 24, 1859:

Footage of the moth that pollinates Angraecum sesquipedale, a Madagascar orchid, whose existence Darwin predicted 142 years ago. Because the nectar is so far down the neck of this orchid, Darwin knew that there had to be a species of moth with a “tongue” long enough to pollinate it. And now that moth has been found.